三峡水库香溪河库湾氮磷分布状况及沉积物污染评价

为了解三峡大坝蓄水完成之后香溪河库湾水体及沉积物中氮、磷的分布状况以及沉积物污染水平,2013年4月对三峡水库香溪河库湾进行调查采样,测定表层水及沉积物中氮磷含量和形态组成。结果表明,香溪河库湾表层水总磷(TP)含量范围为0.20~0.51 mg·L~(-1),总氮(TN)含量范围为0.54~2.25 mg·L~(-1),TP主要由磷酸盐(PO_4~(3-))组成,TN主要由硝酸盐(NO_3~-)以及氨氮(NH_4~+)组成,TP在空间上呈现从河口向库尾逐渐升高的分布格局,TN分布从河口向库尾逐渐降低。香溪河库湾沉积物中TP含量变化范围为642~1 189 mg·kg~(-1),TN含量变化范围为867~1 718 mg·kg~(-1),沉积物TP含量分布呈现上游高下游低,沉积物TN分布趋势呈现中间高,两头低。沉积物中TP主要由无机磷(IP)组成,有机磷(OP)所占比例较小,其中IP由钙磷(Ca-P)、铁铝磷(Fe/Al-P)组成,三者含量:Ca-POPFe/Al-P,且沉积物TP含量空间变化受到三者影响(P0.05)。采用单一因子标准指数法对香溪河库湾沉积物中TN、TP污染水平进行评价,结果表明,表层沉积物中TN、TP最低级别污染指数平均值为2.0和1.6,表层沉积物中TN、TP污染指数均超过最低污染水平,且TP的严重级别污染指数达到0.5以上。三峡水库三期蓄水完成以后,香溪河库湾表层水体中氮磷含量较初期蓄水有所升高,各样点沉积物中氮磷含量表现出相同的趋势,沉积物中不稳定磷释放对水体富营养化具有影响,香溪河库湾的表层沉积物已经受到一定的污染,磷污染水平较高。

Spatial Distribution of Nitrogen and Phosphorus, and Pollution Evaluation for Sediment in Xiangxi Bay, Three Gorges Reservoir

In order to investigate the nitrogen and phosphorus spatial distribution in the water and sediment , the pollution evaluation for sediment of Xiangxi Bay after the impoundment of the Three Gorges Dam, investigation and sampling were performed in Xiangxi Bay of the Three Gorges Reservoir in April 2013, the content and morphology of nitrogen and phosphorus in the surface water and sediment were analyzed. The results showed that the total phosphorus (TP) content of surface water in Xiangxi Bay was 0.20-0.51 mg L^-1, and the total nitrogen (TN) content was 0.54-2.25 mg L^-1. The TP consists mainly of phosphates (PO₄^3-), and the TN consists mainly of nitrate (NO₃^-) and ammonia (NH₄⁺). The TP content increased gradually from the estuary to the end of reservoir in the spatial distribution and the TN gradually decreases from the estuary to the end of the reservoir. The range of TP content was 642-1 189 mg kg^-1 , and the range of TN content was 867-1 718 mg kg^-1 in surface sediment of Xiangxi Bay. The content of TP in the sediments were higher in the upper reaches of the Bay and the content of TN in the sediments were higher in the middle stretch but lower in the two edges of the Bay. The total phosphorus in sediments is mainly composed of inorganic phosphorus (IP), in which the IP was composed of calcium bound phosphorus (Ca-P) and iron/aluminum bound phosphorus (Fe/Al-P), and the proportion of organic phosphorus (OP) is relatively small. The content of the three forms decreased as: Ca-P>OP>Fe/Al-P. Moreover, the spatial variation of TP contents were affected by the three forms of phosphorus (P<0.05). According to the survey on the pollution level of TN and TP in the sediments of Xiangxi Bay, the average value of the lowest level pollution index of TN and TP in the surface sediments is 2.0 and 1.6, the pollution index of TN and TP exceeds the lowest level of pollution and TP''s severe grade pollution index is over 0.5. After the completion of the second stage of impoundment of the Three Gorges Reservoir, the content of nitrogen and phosphorus in the surface water of Xiangxi Bay was higher than that in the early stage and the content of nitrogen and phosphorus in the sediments showed the same trend. The release of unstable phosphorus in the sediments has an effect on water eutrophication. The surface sediments of Xiangxi Bay have been polluted, and the pollution of nitrogen and phosphorus is relatively serious.